Speed limiters according to the current state of the art usually comprise a speed limiter wheel which is formed with lobes or cams and which can be designed as a separate disc cam or cam disc. This cam disc can also be integrally integrated in a cable pulley which is moved by the limiter cable running together with the elevator car. DE 3615270 shows a speed limiter of that kind. Moreover, there are also constructions in which the cam disc is designed as a guide wheel running together with the car. However, it is common to all of these design variants of speed limiters that when the cam disc rotates the lobes of the cam disc provide at the circumference thereof a wave-shaped or sinusoidally curved sequence of lobes and valleys, which sequence is termed cam track or, in the following, control cam.
The lobes or the control cam acts or act, depending on the rotational speed of the cam disc, counter to the inertia and/or the force of a return spring on a mass which runs by a roller on the cam track or control cam. This mass is usually designed as pawl or as a rotatably mounted pendulum with a pendulum nose which describes a movement on attainment of a specific rotational speed of the cam disc or when the moment of inertia of the pendulum, which is thus set in oscillation, exceeds the restoring moment of the restoring spring.
This movement of the pendulum nose is used, for example, in order to trigger or actuate a pre-contact switch with the help of which the further drive of the elevator car or the counterweight is switched off in advance. The principal system-intrinsic parameters of this principle of triggering, namely the number, arrangement and height of the lobes on the cam disc, the mass inertia of the pendulum and the restraining force of the restoring spring, thus allow, as a first safety step, switching-off of the drive at a specific rotational speed of the cam disc. This specific rotational speed of the cam disc is thus termed pre-contact speed (VCK).
If the rotational speed of the cam disc rises further or the pre-contact speed is exceeded and a trigger speed (VCA) is reached, then the pendulum nose of the same pendulum or also of a second pendulum detents in recesses or blocking cams or detent lugs, which are provided therefor, and thereby blocks the cable pulley of the limiter cable. This blocking of the cable pulley of the limiter cable in turn has the consequence that a friction force builds up between the cable pulley and the limiter cable and in turn triggers, as a second safety step, the safety brake device of the elevator car.
The triggering of the safety brake device ultimately takes place through a tension force (FC) which arises in the limiter cable due to the friction between the limiter cable and the cable pulley. This tension force is used, in the case of a single-acting speed limiter system, by means of a trigger mechanism only for triggering of the safety brake device in the event of downward movements of the elevator car. In the case of a double-acting speed limiter system triggering takes place not only for downward movements, but also for upward movements of the elevator car. The trigger mechanism usually comprises a further safety switch which is similarly in a position of interrupting the safety circuit of the elevator control.
A general disadvantage of this principle of construction of a conventional speed limiter system is that only a single specific trigger value, which corresponds with the fixed parameters of the components, can be set at the works. Consequently, it is disadvantageous, for example, that—if, for example, consideration is given only to the mechanical triggering of the safety brake device in itself alone—the elevator installation is usually operated during assembly over a longer test period of time at a reduced speed and in this case the speed limiter system responds only in the case of significantly higher speeds. This can mean that in the event of a risk situation during this test period of time in the assembly phase the safety brake device is triggered only very late or even that the elevator car travels, without braking, onto the shaft buffer at a speed which still lies below the trigger value corresponding with normal operation.
Moreover, it is disadvantageous with conventional speed limiter systems that, particularly in the case of elevator installations conceived and permissible for higher rated speeds such as, for example, VKN=1.5 m/s, the biasing of the restraining spring has to have substantial values. This in turn has the consequence that the pendulum exerts large spring forces or reaction forces on the cam disc and on the cable pulley fixedly connected therewith. Depending on the respective setting of the roller of the pendulum on the control cam, i.e. depending on whether the roller just describes the rising path towards the crest point of an individual lobe or just describes the path falling away from the crest point of the lobe, the high restraining forces manifest themselves as a deceleration or acceleration of the rotational speed of the cam disc. These inconstancies or periodic deviations of the rotational speed of the cam disc from a constant rotational speed are transmitted to the cable pulley, from this to the limiter cable and from this to the elevator car. This leads to deteriorated travel comfort, undesired vibrations, excessive material stressing and output of noise.
By way of example, measurements have shown that the cause of car vibrations is attributable to the speed limiter or the number, arrangement and design of the lobes of the cam disc and the rotational speed of the cam disc. Thus, for example, specific embodiments of elevator installations of the applicant manufacturer have a car vibration maximum value of 19 Hertz. In the case of an exemplifying cable pulley diameter D of 0.2 m or a cable pulley circumference U of D·π=0.628 m and an exemplifying elevator car rated speed VKN of 1.5 m/s an angular speed ω=VKN/U=1.5/0.628=2.388 s−1 results therefrom. In the case of, for example, eight lobes on the cam disc this gives a frequency f=2.388·8=19.1 Hertz. The frequency f of the cable pulley is thus provably the excitation frequency for the measured car vibrations.
A further disadvantage of known speed limiters is that they only insufficiently satisfy the demands of elevator installations without engine rooms such as are currently ever more frequently desired. Thus, the omission of the engine room has, for example, the effect that an unrestricted capability of access to the speed limiter itself is no longer ensured and thus new possibilities or new interfaces at the speed limiter for installation, for setting—whether at the time of initial installation or at the time of later normal operation or at the time of maintenance work—and for triggering in cases of risk and for resetting after triggering has taken place have to be provided.